When it is assumed that air containing foreign matters such as liquid droplets of water or oil or solid particles is handled as air to be treated, the foreign matters contained in the air can be separated and removed on the basis of differences in specific gravity and in centrifugal force between the air and the foreign matters in the swirling of the air to be treated. A technique which separates and removes the foreign matters by utilizing such a difference in centrifugal force is used for a centrifugal, a filter, a cleaner, and others.
An electric cleaner adapted to swirl air containing dusts sucked from a suction port by a swirl unit is disclosed in Patent Document 1. A filter adapted to swirl liquid in order to remove foreign matters mixed in liquid coolant is disclosed in Patent Document 2.